wc -l medals.txt
grep "中国" medals.txt | sort -k2,2nr -k3,3nr -k4,4nr
sort -t',' -k4 -nr medals.txt | head -n 5 | cut -d',' -f1
sort -t',' -k2 -nr medals.txt | head -n 5 | awk -F',' '{sum += $2} END {print sum}'
